Initial vendor packages

Signed-off-by: Valentin Popov <valentin@popov.link>

1 files changed, 988 insertions, 0 deletions

diff --git a/vendor/exr/src/compression/piz/huffman.rs b/vendor/exr/src/compression/piz/huffman.rs
new file mode 100644
index 0000000..a01cbf2
--- /dev/null
+++ b/vendor/exr/src/compression/piz/huffman.rs
@@ -0,0 +1,988 @@
+//! 16-bit Huffman compression and decompression.
+//! Huffman compression and decompression routines written
+//!	by Christian Rouet for his PIZ image file format.
+// see https://github.com/AcademySoftwareFoundation/openexr/blob/88246d991e0318c043e6f584f7493da08a31f9f8/OpenEXR/IlmImf/ImfHuf.cpp
+
+use crate::math::RoundingMode;
+use crate::error::{Error, Result, UnitResult, u64_to_usize, u32_to_usize};
+use crate::io::Data;
+use std::{
+    cmp::Ordering,
+    collections::BinaryHeap,
+    io::{Cursor, Read, Write},
+};
+use std::convert::TryFrom;
+use smallvec::SmallVec;
+
+
+pub fn decompress(compressed: &[u8], expected_size: usize) -> Result<Vec<u16>> {
+    let mut remaining_compressed = compressed;
+
+    let min_code_index = usize::try_from(u32::read(&mut remaining_compressed)?)?;
+    let max_code_index_32 = u32::read(&mut remaining_compressed)?;
+    let _table_size = usize::try_from(u32::read(&mut remaining_compressed)?)?; // TODO check this and return Err?
+    let bit_count = usize::try_from(u32::read(&mut remaining_compressed)?)?;
+    let _skipped = u32::read(&mut remaining_compressed)?; // what is this
+
+    let max_code_index = usize::try_from(max_code_index_32).unwrap();
+    if min_code_index >= ENCODING_TABLE_SIZE || max_code_index >= ENCODING_TABLE_SIZE {
+        return Err(Error::invalid(INVALID_TABLE_SIZE));
+    }
+
+    if RoundingMode::Up.divide(bit_count, 8) > remaining_compressed.len() {
+        return Err(Error::invalid(NOT_ENOUGH_DATA));
+    }
+
+    let encoding_table = read_encoding_table(&mut remaining_compressed, min_code_index, max_code_index)?;
+    if bit_count > 8 * remaining_compressed.len() { return Err(Error::invalid(INVALID_BIT_COUNT)); }
+
+    let decoding_table = build_decoding_table(&encoding_table, min_code_index, max_code_index)?;
+
+    let result = decode_with_tables(
+        &encoding_table,
+        &decoding_table,
+        &remaining_compressed,
+        i32::try_from(bit_count)?,
+        max_code_index_32,
+        expected_size,
+    )?;
+
+    Ok(result)
+}
+
+pub fn compress(uncompressed: &[u16]) -> Result<Vec<u8>> {
+    if uncompressed.is_empty() { return Ok(vec![]); }
+
+    let mut frequencies = count_frequencies(uncompressed);
+    let (min_code_index, max_code_index) = build_encoding_table(&mut frequencies);
+
+    let mut result = Cursor::new(Vec::with_capacity(uncompressed.len()));
+    u32::write_slice(&mut result, &[0; 5])?; // we come back to these later after we know more about the compressed data
+
+    let table_start = result.position();
+    pack_encoding_table(
+        &frequencies,
+        min_code_index,
+        max_code_index,
+        &mut result,
+    )?;
+
+    let data_start = result.position();
+    let bit_count = encode_with_frequencies(
+        &frequencies,
+        uncompressed,
+        max_code_index,
+        &mut result
+    )?;
+
+    // write meta data after this
+    result.set_position(0);
+    let table_length = data_start - table_start;
+
+    u32::try_from(min_code_index)?.write(&mut result)?;
+    u32::try_from(max_code_index)?.write(&mut result)?;
+    u32::try_from(table_length)?.write(&mut result)?;
+    u32::try_from(bit_count)?.write(&mut result)?;
+    0_u32.write(&mut result)?;
+
+    Ok(result.into_inner())
+}
+
+
+const ENCODE_BITS: u64 = 16; // literal (value) bit length
+const DECODE_BITS: u64 = 14; // decoding bit size (>= 8)
+
+const ENCODING_TABLE_SIZE: usize = ((1 << ENCODE_BITS) + 1) as usize;
+const DECODING_TABLE_SIZE: usize = (1 << DECODE_BITS) as usize;
+const DECODE_MASK: u64 = DECODING_TABLE_SIZE as u64 - 1;
+
+const SHORT_ZEROCODE_RUN: u64 = 59;
+const LONG_ZEROCODE_RUN: u64 = 63;
+const SHORTEST_LONG_RUN: u64 = 2 + LONG_ZEROCODE_RUN - SHORT_ZEROCODE_RUN;
+const LONGEST_LONG_RUN: u64 = 255 + SHORTEST_LONG_RUN;
+
+
+#[derive(Clone, Debug, Eq, PartialEq)]
+enum Code {
+    Empty,
+    Short(ShortCode),
+    Long(SmallVec<[u32; 2]>), // often 2, sometimes 4, rarely 8
+}
+
+#[derive(Clone, Debug, Eq, PartialEq)]
+struct ShortCode {
+    value: u32,
+    len: u8,
+}
+
+impl ShortCode {
+    #[inline] fn len(&self) -> u64 { u64::from(self.len) }
+}
+
+/// Decode (uncompress) n bits based on encoding & decoding tables:
+fn decode_with_tables(
+    encoding_table: &[u64],
+    decoding_table: &[Code],
+    mut input: &[u8],
+    input_bit_count: i32,
+    run_length_code: u32,
+    expected_output_size: usize,
+) -> Result<Vec<u16>>
+{
+    let mut output = Vec::with_capacity(expected_output_size);
+    let mut code_bits = 0_u64;
+    let mut code_bit_count = 0_u64;
+
+    while input.len() > 0 {
+        read_byte(&mut code_bits, &mut code_bit_count, &mut input)?;
+
+        // Access decoding table
+        while code_bit_count >= DECODE_BITS {
+            let code_index = (code_bits >> (code_bit_count - DECODE_BITS)) & DECODE_MASK;
+            let code = &decoding_table[u64_to_usize(code_index)];
+
+            // Get short code
+            if let Code::Short(code) = code {
+                code_bit_count -= code.len();
+
+                read_code_into_vec(
+                    code.value,
+                    run_length_code,
+                    &mut code_bits,
+                    &mut code_bit_count,
+                    &mut input,
+                    &mut output,
+                    expected_output_size,
+                )?;
+            }
+            else if let Code::Long(ref long_codes) = code {
+                debug_assert_ne!(long_codes.len(), 0);
+
+                let long_code = long_codes.iter()
+                    .filter_map(|&long_code|{
+                        let encoded_long_code = encoding_table[u32_to_usize(long_code)];
+                        let length = length(encoded_long_code);
+
+                        while code_bit_count < length && input.len() > 0 {
+                            let err = read_byte(&mut code_bits, &mut code_bit_count, &mut input);
+                            if let Err(err) = err { return Some(Err(err)); }
+                        }
+
+                        if code_bit_count >= length {
+                            let required_code = (code_bits >> (code_bit_count - length)) & ((1 << length) - 1);
+
+                            if self::code(encoded_long_code) == required_code {
+                                code_bit_count -= length;
+                                return Some(Ok(long_code));
+                            }
+                        }
+
+                        None
+
+                    })
+                    .next()
+                    .ok_or(Error::invalid(INVALID_CODE))?;
+
+                read_code_into_vec(
+                    long_code?,
+                    run_length_code,
+                    &mut code_bits,
+                    &mut code_bit_count,
+                    &mut input,
+                    &mut output,
+                    expected_output_size,
+                )?;
+            }
+            else {
+                return Err(Error::invalid(INVALID_CODE));
+            }
+        }
+    }
+
+    let count = u64::try_from((8 - input_bit_count) & 7)?;
+    code_bits >>= count;
+    code_bit_count -= count;
+
+    while code_bit_count > 0 {
+        let index = (code_bits << (DECODE_BITS - code_bit_count)) & DECODE_MASK;
+        let code = &decoding_table[u64_to_usize(index)];
+
+        if let Code::Short(short_code) = code {
+            if short_code.len() > code_bit_count { return Err(Error::invalid("code")) }; // FIXME why does this happen??
+            code_bit_count -= short_code.len(); // FIXME may throw "attempted to subtract with overflow"
+
+            read_code_into_vec(
+                short_code.value,
+                run_length_code,
+                &mut code_bits,
+                &mut code_bit_count,
+                &mut input,
+                &mut output,
+                expected_output_size,
+            )?;
+        }
+        else {
+            return Err(Error::invalid(INVALID_CODE));
+        }
+    }
+
+    if output.len() != expected_output_size {
+        return Err(Error::invalid(NOT_ENOUGH_DATA));
+    }
+
+    Ok(output)
+}
+
+/// Build a decoding hash table based on the encoding table code:
+///	- short codes (<= HUF_DECBITS) are resolved with a single table access;
+///	- long code entry allocations are not optimized, because long codes are
+///	  unfrequent;
+///	- decoding tables are used by hufDecode();
+fn build_decoding_table(
+    encoding_table: &[u64],
+    min_code_index: usize,
+    max_code_index: usize,
+) -> Result<Vec<Code>>
+{
+    let mut decoding_table = vec![Code::Empty; DECODING_TABLE_SIZE]; // not an array because of code not being copy
+
+    for (code_index, &encoded_code) in encoding_table[..= max_code_index].iter().enumerate().skip(min_code_index) {
+        let code_index = u32::try_from(code_index).unwrap();
+
+        let code = code(encoded_code);
+        let length = length(encoded_code);
+
+        if code >> length != 0 {
+            return Err(Error::invalid(INVALID_TABLE_ENTRY));
+        }
+
+        if length > DECODE_BITS {
+            let long_code = &mut decoding_table[u64_to_usize(code >> (length - DECODE_BITS))];
+
+            match long_code {
+                Code::Empty => *long_code = Code::Long(smallvec![code_index]),
+                Code::Long(lits) => lits.push(code_index),
+                _ => { return Err(Error::invalid(INVALID_TABLE_ENTRY)); }
+            }
+        }
+        else if length != 0 {
+            let default_value = Code::Short(ShortCode {
+                value: code_index,
+                len: length as u8,
+            });
+
+            let start_index = u64_to_usize(code << (DECODE_BITS - length));
+            let count = u64_to_usize(1 << (DECODE_BITS - length));
+
+            for value in &mut decoding_table[start_index .. start_index + count] {
+                *value = default_value.clone();
+            }
+        }
+    }
+
+    Ok(decoding_table)
+}
+
+/// Run-length-decompresses all zero runs from the packed table to the encoding table
+fn read_encoding_table(
+    packed: &mut impl Read,
+    min_code_index: usize,
+    max_code_index: usize,
+) -> Result<Vec<u64>>
+{
+    let mut code_bits = 0_u64;
+    let mut code_bit_count = 0_u64;
+
+    // TODO push() into encoding table instead of index stuff?
+        let mut encoding_table = vec![0_u64; ENCODING_TABLE_SIZE];
+    let mut code_index = min_code_index;
+    while code_index <= max_code_index {
+        let code_len = read_bits(6, &mut code_bits, &mut code_bit_count, packed)?;
+        encoding_table[code_index] = code_len;
+
+        if code_len == LONG_ZEROCODE_RUN {
+            let zerun_bits = read_bits(8, &mut code_bits, &mut code_bit_count, packed)?;
+            let zerun = usize::try_from(zerun_bits + SHORTEST_LONG_RUN).unwrap();
+
+            if code_index + zerun > max_code_index + 1 {
+                return Err(Error::invalid(TABLE_TOO_LONG));
+            }
+
+            for value in &mut encoding_table[code_index..code_index + zerun] {
+                *value = 0;
+            }
+
+            code_index += zerun;
+        }
+        else if code_len >= SHORT_ZEROCODE_RUN {
+            let duplication_count = usize::try_from(code_len - SHORT_ZEROCODE_RUN + 2).unwrap();
+            if code_index + duplication_count > max_code_index + 1 {
+                return Err(Error::invalid(TABLE_TOO_LONG));
+            }
+
+            for value in &mut encoding_table[code_index .. code_index + duplication_count] {
+                *value = 0;
+            }
+
+            code_index += duplication_count;
+        }
+        else {
+            code_index += 1;
+        }
+    }
+
+    build_canonical_table(&mut encoding_table);
+    Ok(encoding_table)
+}
+
+// TODO Use BitStreamReader for all the bit reads?!
+#[inline]
+fn read_bits(
+    count: u64,
+    code_bits: &mut u64,
+    code_bit_count: &mut u64,
+    input: &mut impl Read,
+) -> Result<u64>
+{
+    while *code_bit_count < count {
+        read_byte(code_bits, code_bit_count, input)?;
+    }
+
+    *code_bit_count -= count;
+    Ok((*code_bits >> *code_bit_count) & ((1 << count) - 1))
+}
+
+#[inline]
+fn read_byte(code_bits: &mut u64, bit_count: &mut u64, input: &mut impl Read) -> UnitResult {
+    *code_bits = (*code_bits << 8) | u8::read(input)? as u64;
+    *bit_count += 8;
+    Ok(())
+}
+
+#[inline]
+fn read_code_into_vec(
+    code: u32,
+    run_length_code: u32,
+    code_bits: &mut u64,
+    code_bit_count: &mut u64,
+    read: &mut impl Read,
+    out: &mut Vec<u16>,
+    max_len: usize,
+) -> UnitResult
+{
+    if code == run_length_code { // code may be too large for u16
+        if *code_bit_count < 8 {
+            read_byte(code_bits, code_bit_count, read)?;
+        }
+
+        *code_bit_count -= 8;
+
+        let code_repetitions = usize::from((*code_bits >> *code_bit_count) as u8);
+
+        if out.len() + code_repetitions > max_len {
+            return Err(Error::invalid(TOO_MUCH_DATA));
+        }
+        else if out.is_empty() {
+            return Err(Error::invalid(NOT_ENOUGH_DATA));
+        }
+
+        let repeated_code = *out.last().unwrap();
+        out.extend(std::iter::repeat(repeated_code).take(code_repetitions));
+    }
+    else if out.len() < max_len { // implies that code is not larger than u16???
+        out.push(u16::try_from(code)?);
+    }
+    else {
+        return Err(Error::invalid(TOO_MUCH_DATA));
+    }
+
+    Ok(())
+}
+
+fn count_frequencies(data: &[u16]) -> Vec<u64> {
+    let mut frequencies = vec![0_u64; ENCODING_TABLE_SIZE];
+
+    for value in data {
+        frequencies[*value as usize] += 1;
+    }
+
+    frequencies
+}
+
+fn write_bits(
+    count: u64,
+    bits: u64,
+    code_bits: &mut u64,
+    code_bit_count: &mut u64,
+    mut out: impl Write,
+) -> UnitResult
+{
+    *code_bits = (*code_bits << count) | bits;
+    *code_bit_count += count;
+
+    while *code_bit_count >= 8 {
+        *code_bit_count -= 8;
+        out.write(&[
+            (*code_bits >> *code_bit_count) as u8 // TODO make sure never or always wraps?
+        ])?;
+    }
+
+    Ok(())
+}
+
+fn write_code(scode: u64, code_bits: &mut u64, code_bit_count: &mut u64, mut out: impl Write) -> UnitResult {
+    write_bits(length(scode), code(scode), code_bits, code_bit_count, &mut out)
+}
+
+#[inline(always)]
+fn send_code(
+    scode: u64,
+    run_count: u64,
+    run_code: u64,
+    code_bits: &mut u64,
+    code_bit_count: &mut u64,
+    mut out: impl Write,
+) -> UnitResult
+{
+    // Output a run of runCount instances of the symbol sCount.
+    // Output the symbols explicitly, or if that is shorter, output
+    // the sCode symbol once followed by a runCode symbol and runCount
+    // expressed as an 8-bit number.
+    if length(scode) + length(run_code) + 8 < length(scode) * run_count {
+        write_code(scode, code_bits, code_bit_count, &mut out)?;
+        write_code(run_code, code_bits, code_bit_count, &mut out)?;
+        write_bits(8, run_count, code_bits, code_bit_count, &mut out)?;
+    }
+    else {
+        for _ in 0 ..= run_count {
+            write_code(scode, code_bits, code_bit_count, &mut out)?;
+        }
+    }
+
+    Ok(())
+}
+
+fn encode_with_frequencies(
+    frequencies: &[u64],
+    uncompressed: &[u16],
+    run_length_code: usize,
+    mut out: &mut Cursor<Vec<u8>>,
+) -> Result<u64>
+{
+    let mut code_bits = 0;
+    let mut code_bit_count = 0;
+
+    let mut run_start_value = uncompressed[0];
+    let mut run_length = 0;
+
+    let start_position = out.position();
+
+    // Loop on input values
+    for &current_value in &uncompressed[1..] {
+        // Count same values or send code
+        if run_start_value == current_value && run_length < 255 {
+            run_length += 1;
+        }
+        else {
+            send_code(
+                frequencies[run_start_value as usize],
+                run_length,
+                frequencies[run_length_code],
+                &mut code_bits,
+                &mut code_bit_count,
+                &mut out,
+            )?;
+
+            run_length = 0;
+        }
+
+        run_start_value = current_value;
+    }
+
+    // Send remaining code
+    send_code(
+        frequencies[run_start_value as usize],
+        run_length,
+        frequencies[run_length_code],
+        &mut code_bits,
+        &mut code_bit_count,
+        &mut out,
+    )?;
+
+    let data_length = out.position() - start_position; // we shouldn't count the last byte write
+
+    if code_bit_count != 0 {
+        out.write(&[
+            (code_bits << (8 - code_bit_count) & 0xff) as u8
+        ])?;
+    }
+
+    Ok(data_length * 8 + code_bit_count)
+}
+
+///
+/// Pack an encoding table:
+///	- only code lengths, not actual codes, are stored
+///	- runs of zeroes are compressed as follows:
+///
+///	  unpacked		packed
+///	  --------------------------------
+///	  1 zero		0	(6 bits)
+///	  2 zeroes		59
+///	  3 zeroes		60
+///	  4 zeroes		61
+///	  5 zeroes		62
+///	  n zeroes (6 or more)	63 n-6	(6 + 8 bits)
+///
+fn pack_encoding_table(
+    frequencies: &[u64],
+    min_index: usize,
+    max_index: usize,
+    mut out: &mut Cursor<Vec<u8>>,
+) -> UnitResult
+{
+    let mut code_bits = 0_u64;
+    let mut code_bit_count = 0_u64;
+
+    let mut frequency_index = min_index;
+    while frequency_index <= max_index { // TODO slice iteration?
+        let code_length = length(frequencies[frequency_index]);
+
+        if code_length == 0 {
+            let mut zero_run = 1;
+
+            while frequency_index < max_index && zero_run < LONGEST_LONG_RUN {
+                if length(frequencies[frequency_index + 1]) > 0 {
+                    break;
+                }
+
+                frequency_index += 1;
+                zero_run += 1;
+            }
+
+            if zero_run >= 2 {
+                if zero_run >= SHORTEST_LONG_RUN {
+                    write_bits(6, LONG_ZEROCODE_RUN, &mut code_bits, &mut code_bit_count, &mut out)?;
+                    write_bits(8, zero_run - SHORTEST_LONG_RUN, &mut code_bits, &mut code_bit_count, &mut out)?;
+                }
+                else {
+                    write_bits(6, SHORT_ZEROCODE_RUN + zero_run - 2, &mut code_bits, &mut code_bit_count, &mut out)?;
+                }
+
+                frequency_index += 1; // we must increment or else this may go very wrong
+                continue;
+            }
+        }
+
+        write_bits(6, code_length, &mut code_bits, &mut code_bit_count, &mut out)?;
+        frequency_index += 1;
+    }
+
+    if code_bit_count > 0 {
+        out.write(&[
+            (code_bits << (8 - code_bit_count)) as u8
+        ])?;
+    }
+
+    Ok(())
+}
+
+/// Build a "canonical" Huffman code table:
+///	- for each (uncompressed) symbol, code contains the length
+///	  of the corresponding code (in the compressed data)
+///	- canonical codes are computed and stored in code
+///	- the rules for constructing canonical codes are as follows:
+///	  * shorter codes (if filled with zeroes to the right)
+///	    have a numerically higher value than longer codes
+///	  * for codes with the same length, numerical values
+///	    increase with numerical symbol values
+///	- because the canonical code table can be constructed from
+///	  symbol lengths alone, the code table can be transmitted
+///	  without sending the actual code values
+///	- see http://www.compressconsult.com/huffman/
+fn build_canonical_table(code_table: &mut [u64]) {
+    debug_assert_eq!(code_table.len(), ENCODING_TABLE_SIZE);
+
+    let mut count_per_code = [0_u64; 59];
+
+    for &code in code_table.iter() {
+        count_per_code[u64_to_usize(code)] += 1;
+    }
+
+    // For each i from 58 through 1, compute the
+    // numerically lowest code with length i, and
+    // store that code in n[i].
+    {
+        let mut code = 0_u64; // TODO use foldr?
+        for count in &mut count_per_code.iter_mut().rev() {
+            let next_code = (code + *count) >> 1;
+            *count = code;
+            code = next_code;
+        }
+    }
+
+    // code[i] contains the length, l, of the
+    // code for symbol i.  Assign the next available
+    // code of length l to the symbol and store both
+    // l and the code in code[i]. // TODO iter + filter ?
+    for symbol_length in code_table.iter_mut() {
+        let current_length = *symbol_length;
+        let code_index = u64_to_usize(current_length);
+        if current_length > 0 {
+            *symbol_length = current_length | (count_per_code[code_index] << 6);
+            count_per_code[code_index] += 1;
+        }
+    }
+}
+
+
+/// Compute Huffman codes (based on frq input) and store them in frq:
+///	- code structure is : [63:lsb - 6:msb] | [5-0: bit length];
+///	- max code length is 58 bits;
+///	- codes outside the range [im-iM] have a null length (unused values);
+///	- original frequencies are destroyed;
+///	- encoding tables are used by hufEncode() and hufBuildDecTable();
+///
+/// NB: The following code "(*a == *b) && (a > b))" was added to ensure
+///     elements in the heap with the same value are sorted by index.
+///     This is to ensure, the STL make_heap()/pop_heap()/push_heap() methods
+///     produced a resultant sorted heap that is identical across OSes.
+fn build_encoding_table(
+    frequencies: &mut [u64], // input frequencies, output encoding table
+) -> (usize, usize) // return frequency max min range
+{
+    debug_assert_eq!(frequencies.len(), ENCODING_TABLE_SIZE);
+
+    /// Frequency with position, used for MinHeap.
+    #[derive(Eq, PartialEq, Copy, Clone)]
+    struct HeapFrequency {
+        position: usize,
+        frequency: u64,
+    }
+
+    impl Ord for HeapFrequency {
+        fn cmp(&self, other: &Self) -> Ordering {
+            other.frequency.cmp(&self.frequency)
+                .then_with(|| other.position.cmp(&self.position))
+        }
+    }
+
+    impl PartialOrd for HeapFrequency {
+        fn partial_cmp(&self, other: &Self) -> Option<Ordering> { Some(self.cmp(other)) }
+    }
+
+    // This function assumes that when it is called, array frq
+    // indicates the frequency of all possible symbols in the data
+    // that are to be Huffman-encoded.  (frq[i] contains the number
+    // of occurrences of symbol i in the data.)
+    //
+    // The loop below does three things:
+    //
+    // 1) Finds the minimum and maximum indices that point
+    //    to non-zero entries in frq:
+    //
+    //     frq[im] != 0, and frq[i] == 0 for all i < im
+    //     frq[iM] != 0, and frq[i] == 0 for all i > iM
+    //
+    // 2) Fills array fHeap with pointers to all non-zero
+    //    entries in frq.
+    //
+    // 3) Initializes array hlink such that hlink[i] == i
+    //    for all array entries.
+
+    // We need to use vec here or we overflow the stack.
+    let mut links = vec![0_usize; ENCODING_TABLE_SIZE];
+    let mut frequency_heap = vec![0_usize; ENCODING_TABLE_SIZE];
+
+    // This is a good solution since we don't have usize::MAX items (no panics or UB),
+    // and since this is short-circuit, it stops at the first in order non zero element.
+    let min_frequency_index = frequencies.iter().position(|f| *f != 0).unwrap_or(0);
+
+    let mut max_frequency_index = 0;
+    let mut frequency_count = 0;
+
+    // assert bounds check to optimize away bounds check in loops
+    assert!(links.len() >= ENCODING_TABLE_SIZE);
+    assert!(frequencies.len() >= ENCODING_TABLE_SIZE);
+
+    for index in min_frequency_index..ENCODING_TABLE_SIZE {
+        links[index] = index; // TODO for x in links.iter().enumerate()
+
+        if frequencies[index] != 0 {
+            frequency_heap[frequency_count] = index;
+            max_frequency_index = index;
+            frequency_count += 1;
+        }
+    }
+
+
+    // Add a pseudo-symbol, with a frequency count of 1, to frq;
+    // adjust the fHeap and hlink array accordingly.  Function
+    // hufEncode() uses the pseudo-symbol for run-length encoding.
+
+    max_frequency_index += 1;
+    frequencies[max_frequency_index] = 1;
+    frequency_heap[frequency_count] = max_frequency_index;
+    frequency_count += 1;
+
+    // Build an array, scode, such that scode[i] contains the number
+    // of bits assigned to symbol i.  Conceptually this is done by
+    // constructing a tree whose leaves are the symbols with non-zero
+    // frequency:
+    //
+    //     Make a heap that contains all symbols with a non-zero frequency,
+    //     with the least frequent symbol on top.
+    //
+    //     Repeat until only one symbol is left on the heap:
+    //
+    //         Take the two least frequent symbols off the top of the heap.
+    //         Create a new node that has first two nodes as children, and
+    //         whose frequency is the sum of the frequencies of the first
+    //         two nodes.  Put the new node back into the heap.
+    //
+    // The last node left on the heap is the root of the tree.  For each
+    // leaf node, the distance between the root and the leaf is the length
+    // of the code for the corresponding symbol.
+    //
+    // The loop below doesn't actually build the tree; instead we compute
+    // the distances of the leaves from the root on the fly.  When a new
+    // node is added to the heap, then that node's descendants are linked
+    // into a single linear list that starts at the new node, and the code
+    // lengths of the descendants (that is, their distance from the root
+    // of the tree) are incremented by one.
+    let mut heap = BinaryHeap::with_capacity(frequency_count);
+    for index in frequency_heap.drain(..frequency_count) {
+        heap.push(HeapFrequency { position: index, frequency: frequencies[index] });
+    }
+
+    let mut s_code = vec![0_u64; ENCODING_TABLE_SIZE];
+
+    while frequency_count > 1 {
+        // Find the indices, mm and m, of the two smallest non-zero frq
+        // values in fHeap, add the smallest frq to the second-smallest
+        // frq, and remove the smallest frq value from fHeap.
+        let (high_position, low_position) = {
+            let smallest_frequency = heap.pop().expect("heap empty bug");
+            frequency_count -= 1;
+
+            let mut second_smallest_frequency = heap.peek_mut().expect("heap empty bug");
+            second_smallest_frequency.frequency += smallest_frequency.frequency;
+
+            (second_smallest_frequency.position, smallest_frequency.position)
+        };
+
+        // The entries in scode are linked into lists with the
+        // entries in hlink serving as "next" pointers and with
+        // the end of a list marked by hlink[j] == j.
+        //
+        // Traverse the lists that start at scode[m] and scode[mm].
+        // For each element visited, increment the length of the
+        // corresponding code by one bit. (If we visit scode[j]
+        // during the traversal, then the code for symbol j becomes
+        // one bit longer.)
+        //
+        // Merge the lists that start at scode[m] and scode[mm]
+        // into a single list that starts at scode[m].
+
+        // Add a bit to all codes in the first list.
+        let mut index = high_position; // TODO fold()
+        loop {
+            s_code[index] += 1;
+            debug_assert!(s_code[index] <= 58);
+
+            // merge the two lists
+            if links[index] == index {
+                links[index] = low_position;
+                break;
+            }
+
+            index = links[index];
+        }
+
+        // Add a bit to all codes in the second list
+        let mut index = low_position; // TODO fold()
+        loop {
+            s_code[index] += 1;
+            debug_assert!(s_code[index] <= 58);
+
+            if links[index] == index {
+                break;
+            }
+
+            index = links[index];
+        }
+    }
+
+    // Build a canonical Huffman code table, replacing the code
+    // lengths in scode with (code, code length) pairs.  Copy the
+    // code table from scode into frq.
+    build_canonical_table(&mut s_code);
+    frequencies.copy_from_slice(&s_code);
+
+    (min_frequency_index, max_frequency_index)
+}
+
+
+#[inline] fn length(code: u64) -> u64 { code & 63 }
+#[inline] fn code(code: u64) -> u64 { code >> 6 }
+
+const INVALID_BIT_COUNT: &'static str = "invalid number of bits";
+const INVALID_TABLE_ENTRY: &'static str = "invalid code table entry";
+const NOT_ENOUGH_DATA: &'static str = "decoded data are shorter than expected";
+const INVALID_TABLE_SIZE: &'static str = "unexpected end of code table data";
+const TABLE_TOO_LONG: &'static str = "code table is longer than expected";
+const INVALID_CODE: &'static str = "invalid code";
+const TOO_MUCH_DATA: &'static str = "decoded data are longer than expected";
+
+
+#[cfg(test)]
+mod test {
+    use super::*;
+    use rand::{Rng, SeedableRng};
+
+    const UNCOMPRESSED_ARRAY: [u16; 100] = [
+        3852, 2432, 33635, 49381, 10100, 15095, 62693, 63738, 62359, 5013, 7715, 59875, 28182,
+        34449, 19983, 20399, 63407, 29486, 4877, 26738, 44815, 14042, 46091, 48228, 25682, 35412,
+        7582, 65069, 6632, 54124, 13798, 27503, 52154, 61961, 30474, 46880, 39097, 15754, 52897,
+        42371, 54053, 14178, 48276, 34591, 42602, 32126, 42062, 31474, 16274, 55991, 2882, 17039,
+        56389, 20835, 57057, 54081, 3414, 33957, 52584, 10222, 25139, 40002, 44980, 1602, 48021,
+        19703, 6562, 61777, 41582, 201, 31253, 51790, 15888, 40921, 3627, 12184, 16036, 26349,
+        3159, 29002, 14535, 50632, 18118, 33583, 18878, 59470, 32835, 9347, 16991, 21303, 26263,
+        8312, 14017, 41777, 43240, 3500, 60250, 52437, 45715, 61520,
+    ];
+
+    const UNCOMPRESSED_ARRAY_SPECIAL: [u16; 100] = [
+        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 28182,
+        0, 65534, 0, 65534, 0, 65534, 0, 65534, 0, 0, 0, 0, 0,
+        0, 0, 0, 54124, 13798, 27503, 52154, 61961, 30474, 46880, 39097, 15754, 52897,
+        42371, 54053, 14178, 48276, 34591, 42602, 32126, 42062, 31474, 16274, 55991, 2882, 17039,
+        56389, 20835, 57057, 54081, 3414, 33957, 52584, 10222, 25139, 40002, 44980, 1602, 48021,
+        19703, 6562, 61777, 41582, 201, 31253, 51790, 15888, 40921, 3627, 12184, 16036, 26349,
+        3159, 29002, 14535, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+        65534, 65534, 65534, 65534, 65534, 65534, 65534, 65534, 65534,
+    ];
+
+    const COMPRESSED_ARRAY: [u8; 703] = [
+        0xc9, 0x0, 0x0, 0x0, 0x2e, 0xfe, 0x0, 0x0, 0x56, 0x2, 0x0, 0x0, 0xa2, 0x2, 0x0, 0x0, 0x0,
+        0x0, 0x0, 0x0, 0x1f, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xd6, 0x47,
+        0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0x28, 0x1f, 0xff, 0xff, 0xed, 0x87, 0xff, 0xff, 0xf0,
+        0x91, 0xff, 0xf8, 0x1f, 0xf4, 0xf1, 0xff, 0x78, 0x1f, 0xfd, 0xa1, 0xff, 0xff, 0xff, 0xff,
+        0xff, 0xff, 0xfa, 0xc7, 0xfe, 0x4, 0x7f, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+        0xff, 0xed, 0x1f, 0xf3, 0xf1, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xe8, 0x7, 0xfd, 0xf8,
+        0x7f, 0xff, 0xff, 0xff, 0xfd, 0x10, 0x7f, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0x51, 0xff,
+        0xff, 0xff, 0xff, 0xfe, 0x1, 0xff, 0x73, 0x1f, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+        0xff, 0xff, 0xff, 0xff, 0xff, 0xfe, 0x0, 0x7f, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+        0xff, 0xff, 0xff, 0xfc, 0xa4, 0x7f, 0xf5, 0x7, 0xfc, 0x48, 0x7f, 0xe0, 0x47, 0xff, 0xff,
+        0xf5, 0x91, 0xff, 0xff, 0xff, 0xff, 0xf1, 0xf1, 0xff, 0xff, 0xff, 0xff, 0xf8, 0x21, 0xff,
+        0x7f, 0x1f, 0xf8, 0xd1, 0xff, 0xe7, 0x1f, 0xff, 0xff, 0xff, 0xff, 0xbc, 0x1f, 0xf2, 0x91,
+        0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0x1c, 0x1f, 0xff, 0xff, 0xff, 0xff, 0xe7,
+        0x1f, 0xff, 0xff, 0xff, 0xff, 0xff, 0xfc, 0x8c, 0x7f, 0xff, 0xff, 0xc, 0x1f, 0xff, 0xff,
+        0xe5, 0x7, 0xff, 0xff, 0xfa, 0x81, 0xff, 0xff, 0xff, 0x20, 0x7f, 0xff, 0xff, 0xff, 0xff,
+        0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+        0xff, 0xff, 0xff, 0xff, 0xff, 0xfe, 0xbc, 0x7f, 0xff, 0xff, 0xff, 0xfc, 0x38, 0x7f, 0xff,
+        0xff, 0xff, 0xfc, 0xd0, 0x7f, 0xd3, 0xc7, 0xff, 0xff, 0xf7, 0x91, 0xff, 0xff, 0xff, 0xff,
+        0xfe, 0xc1, 0xff, 0xff, 0xff, 0xff, 0xf9, 0x61, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xc7,
+        0x87, 0xff, 0xff, 0xfd, 0x81, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xf1, 0x87, 0xff, 0xff,
+        0xff, 0xff, 0xfe, 0x87, 0xff, 0x58, 0x7f, 0xff, 0xff, 0xff, 0xfd, 0xec, 0x7f, 0xff, 0xff,
+        0xff, 0xfe, 0xd0, 0x7f, 0xff, 0xff, 0xff, 0xff, 0x6c, 0x7f, 0xcb, 0x47, 0xff, 0xff, 0xf3,
+        0x61, 0xff, 0xff, 0xff, 0x80, 0x7f, 0xe1, 0xc7, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0x1f,
+        0x1f, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+        0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0x18, 0x1f, 0xff, 0xff,
+        0xff, 0xff, 0xff, 0xfd, 0xcc, 0x7f, 0xff, 0xff, 0xff, 0xff, 0xff, 0xf8, 0x11, 0xff, 0xff,
+        0xff, 0xff, 0xf8, 0x41, 0xff, 0xbc, 0x1f, 0xff, 0xff, 0xc4, 0x47, 0xff, 0xff, 0xf2, 0x91,
+        0xff, 0xe0, 0x1f, 0xff, 0xff, 0xff, 0xff, 0x6d, 0x1f, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+        0xff, 0xff, 0xff, 0xff, 0xff, 0x2, 0x1f, 0xf9, 0xe1, 0xff, 0xff, 0xff, 0xff, 0xfc, 0xe1,
+        0xff, 0xff, 0xfd, 0xb0, 0x7f, 0xff, 0xff, 0xff, 0xff, 0xff, 0xe1, 0xff, 0xff, 0xff, 0xff,
+        0xff, 0xff, 0xff, 0xff, 0x5a, 0x1f, 0xfc, 0x81, 0xbf, 0x29, 0x1b, 0xff, 0xff, 0xff, 0xff,
+        0xff, 0xff, 0xff, 0xf3, 0x61, 0xbf, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xc8, 0x1b,
+        0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xf6, 0xb1, 0xbf, 0xff, 0xfd, 0x80, 0x6f, 0xff,
+        0xff, 0xf, 0x1b, 0xf8, 0xc1, 0xbf, 0xff, 0xfc, 0xb4, 0x6f, 0xff, 0xff, 0xff, 0xff, 0xff,
+        0xff, 0xff, 0xda, 0x46, 0xfc, 0x54, 0x6f, 0xc9, 0x6, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+        0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0x21, 0x1b, 0xff, 0xff, 0xe0, 0x86, 0xff, 0xff,
+        0xff, 0xff, 0xe2, 0xc6, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+        0xff, 0xff, 0xff, 0xff, 0xff, 0xf3, 0x91, 0xbf, 0xff, 0xfe, 0x24, 0x6f, 0xff, 0xff, 0x6b,
+        0x1b, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xfd, 0xb1, 0xbf, 0xfa, 0x1b, 0xfb, 0x11,
+        0xbf, 0xff, 0xfe, 0x8, 0x6f, 0xff, 0xff, 0x42, 0x1b, 0xff, 0xff, 0xff, 0xff, 0xb9, 0x1b,
+        0xff, 0xff, 0xcf, 0xc6, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xf1, 0x31,
+        0x86, 0x10, 0x9, 0xb4, 0xe4, 0x4c, 0xf7, 0xef, 0x42, 0x87, 0x6a, 0xb5, 0xc2, 0x34, 0x9e,
+        0x2f, 0x12, 0xae, 0x21, 0x68, 0xf2, 0xa8, 0x74, 0x37, 0xe1, 0x98, 0x14, 0x59, 0x57, 0x2c,
+        0x24, 0x3b, 0x35, 0x6c, 0x1b, 0x8b, 0xcc, 0xe6, 0x13, 0x38, 0xc, 0x8e, 0xe2, 0xc, 0xfe,
+        0x49, 0x73, 0xbc, 0x2b, 0x7b, 0x9, 0x27, 0x79, 0x14, 0xc, 0x94, 0x42, 0xf8, 0x7c, 0x1,
+        0x8d, 0x26, 0xde, 0x87, 0x26, 0x71, 0x50, 0x45, 0xc6, 0x28, 0x40, 0xd5, 0xe, 0x8d, 0x8,
+        0x1e, 0x4c, 0xa4, 0x79, 0x57, 0xf0, 0xc3, 0x6d, 0x5c, 0x6d, 0xc0,
+    ];
+
+    fn fill(rng: &mut impl Rng, size: usize) -> Vec<u16> {
+        if rng.gen_bool(0.2) {
+            let value = if rng.gen_bool(0.5) { 0 } else { u16::MAX };
+            return vec![ value; size ];
+        }
+
+        let mut data = vec![0_u16; size];
+
+        data.iter_mut().for_each(|v| {
+            *v = rng.gen_range(0_u16 .. u16::MAX);
+        });
+
+        data
+    }
+
+    /// Test using both input and output from a custom ILM OpenEXR test.
+    #[test]
+    fn compression_comparation() {
+        let raw = compress(&UNCOMPRESSED_ARRAY).unwrap();
+        assert_eq!(raw, COMPRESSED_ARRAY.to_vec());
+    }
+
+    #[test]
+    fn round_trip() {
+        let mut random = rand::rngs::StdRng::from_seed(SEED);
+        let raw = fill(&mut random, u16::MAX as usize);
+
+        let compressed = compress(&raw).unwrap();
+        let uncompressed = decompress(&compressed, raw.len()).unwrap();
+
+        assert_eq!(uncompressed, raw);
+    }
+
+    #[test]
+    fn repetitions_special() {
+        let raw = UNCOMPRESSED_ARRAY_SPECIAL;
+
+        let compressed = compress(&raw).unwrap();
+        let uncompressed = decompress(&compressed, raw.len()).unwrap();
+
+        assert_eq!(uncompressed, raw.to_vec());
+    }
+
+    #[test]
+    fn round_trip100() {
+        let mut random = rand::rngs::StdRng::from_seed(SEED);
+
+        for size_multiplier in 1..10 {
+            let raw = fill(&mut random, size_multiplier * 50_000);
+
+            let compressed = compress(&raw).unwrap();
+            let uncompressed = decompress(&compressed, raw.len()).unwrap();
+
+            assert_eq!(uncompressed, raw);
+        }
+    }
+
+    #[test]
+    fn test_zeroes(){
+        let uncompressed: &[u16] = &[ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 ];
+
+        let compressed = compress(uncompressed).unwrap();
+        let decompressed = decompress(&compressed, uncompressed.len()).unwrap();
+
+        assert_eq!(uncompressed, decompressed.as_slice());
+    }
+
+    const SEED: [u8; 32] = [
+        12,155,32,34,112,109,98,54,
+        12,255,32,34,112,109,98,55,
+        12,155,32,34,12,109,98,54,
+        12,35,32,34,112,109,48,54,
+    ];
+}